maildirpop3d offers multiple POP mailboxes (with
distinct passwords) controlled by a single shell
account. It is a checkpassword replacement, and
sits between qmail-popup and qmail-pop3d. If it
sees a username like "joe-foo", and
~joe/Maildir-foo is a directory, it invokes
qmail-pop3d (as joe) on ~joe/Maildir-foo.
maildirpasswd (included) is then invoked by joe to
set the password for the joe-foo mailbox. The
password is then encrypted and stored.